Trying to Understand the Source of Sky-High Alkalinity and Calcium

[Biokabe]

My water chemistry has been baffling me as of late. Simply put, without any dosing, my calcium and alkalinity levels have been sky-high, my PH has been rather low (though that could just be the probe), and my magnesium levels have been rock-steady.

Specifically, my Alkalinity has been between 10 and 11, and my calcium between 580 and 620. I discontinued dosing over six weeks ago, and the only source of those materials that I have added myself has been with my biweekly water changes - but my replacement water has more typical values of 7 ALK and 440 Calcium.

I am using RO/DI water, and I've tested my water with an ICP test - silica is high (need to replace my DI media), but no calcium or alkalinity in the water.

With the exception of SPS corals (which I've never been able to achieve success with in this tank), the rest of the corals seem to be fine, so it's not that I'm necessarily trying to chase a particular number... just trying to figure out where the elements are coming from and why they never seem to fall despite there not being any discernable source for them to come from.

 

[Randy Holmes-Farley]

How are you measuring alkalinity?

10-11 dKH is not sky high. It's a fine level, as long as you do not have SPS and very low nutrients (nitrate and phosphate).

Some folks with very low demand for calcium and alk find that there is enough slow dissolution of aragonite sand to detectable boost alkalinity.

Declining nitrate will also boost alkalinity.

If you want alkalinity lower, and it is not dropping after a week or two of no additions, then I suggest dropping the alk in your new salt water lower than it is now, and use it for your regular water changes. You can drop it with muriatic acid or sodium bisulfate. The pH will drop too, so you'll need to aerate it to raise the pH back towards "normal".

 

[Biokabe]

How are you measuring alkalinity?

10-11 dKH is not sky high. It's a fine level, as long as you do not have SPS and very low nutrients (nitrate and phosphate).

Some folks with very low demand for calcium and alk find that there is enough slow dissolution of aragonite sand to detectable boost alkalinity.

Declining nitrate will also boost alkalinity.

If you want alkalinity lower, and it is not dropping after a week or two of no additions, then I suggest dropping the alk in your new salt water lower than it is now, and use it for your regular water changes. You can drop it with muriatic acid or sodium bisulfate. The pH will drop too, so you'll need to aerate it to raise the pH back towards "normal".

Thanks!

I'm measuring Alk with three different sources, and I didn't post this until the third came back... I use my Trident as my primary measurement, check it with a Hanna alkalinity meter, and finally with ATI's ICP testing service. They're all within 0.5 dKH of each other, so that's probably a good measurement.

I am trying to keep SPS, so I do want to bring it lower. Nitrate is about 4 ppm, phosphate 0.35 ppm. Is that low enough to cause issues with a higher alkalinity? I hadn't heard about using muriatic acid to lower alkalinity in the make-up water before. If I were to use the bisulfate, I assume I'd want to avoid the mixes for spas or pools - stick to something that's closer to lab grade or 99% pure? Would SeaChem's Acid Buffer do the trick as well?

 

[Randy Holmes-Farley]

There's no reason alk needs to be lower with those nutrient levels, but its also fine to lower it. SPS grows faster at higher alk if sufficient nutrients are present.

Seachem acid buffer (sodium bisulfate) is likely OK.

Some folks use this: